Laser-produced porous surface

ABSTRACT

The present invention disclosed a method of producing a three-dimensional porous tissue in-growth structure. The method includes the steps of depositing a first layer of metal powder and scanning the first layer of metal powder with a laser beam to form a portion of a plurality of predetermined unit cells. Depositing at least one additional layer of metal powder onto a previous layer and repeating the step of scanning a laser beam for at least one of the additional layers in order to continuing forming the predetermined unit cells. The method further includes continuing the depositing and scanning steps to form a medical implant.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/690,307, filed Nov. 21, 2019, which is a continuation ofU.S. patent application Ser. No. 14/671,545, now U.S. Pat. No.10,525,688, filed Mar. 27, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/605,354, now U.S. Pat. No. 8,992,703, filed Sep.6, 2012, which is a continuation-in-part of U.S. patent application Ser.No. 12/843,376, now U.S. Pat. No. 8,268,100, filed Jul. 26, 2010, whichis a continuation of U.S. patent application Ser. No. 12/386,679, nowU.S. Pat. No. 8,268,099, filed Apr. 22, 2009, which is a continuation ofU.S. patent application Ser. No. 10/704,270, now U.S. Pat. No.7,537,664, filed Nov. 7, 2003, which claims the benefit of U.S.Provisional Application No. 60/424,923 filed Nov. 8, 2002, and U.S.Provisional Application No. 60/425,657 filed Nov. 12, 2002. U.S. patentapplication Ser. No. 13/605,354 is also a continuation of U.S. patentapplication Ser. No. 12/846,327 filed Jul. 29, 2010, which is acontinuation of U.S. patent application Ser. No. 11/027,421, nowabandoned, filed Dec. 30, 2004. The entire disclosures of all of theabove-mentioned applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a porous surface and a method forforming the same, which uses a directed energy beam to selectivelyremelt a powder to produce a part. The energy beam may include a laserbeam, and an electron beam or the like. In particular, this inventionrelates to a computer-aided laser apparatus, which sequentially remeltsa plurality of powder layers to form unit cells to build the designedpart in a layer-by-layer fashion. The present application isparticularly directed toward a method of forming a porous and partiallyporous metallic structure.

DESCRIPTION OF THE RELEVANT ART

The field of free-form fabrication has seen many important recentadvances in the fabrication of articles directly from computercontrolled databases. These advances, many of which are in the field ofrapid prototyping of articles such as prototype parts and mold dies,have greatly reduced the time and expense required to fabricatearticles, particularly in contrast to conventional machining processesin which a block of material, such as a metal, is machined according toengineering drawings.

One example of a modern rapid prototyping technology is the selectivelaser sintering process practiced by systems available from DTMCorporation of Austin, Tex. According to this technology, articles areproduced in layer-wise fashion from a laser-fusible powder that isdispensed one layer at a time. The powder is fused, remelted orsintered, by the application of laser energy that is directed inraster-scan fashion to portions of the powder layer corresponding to across section of the article. After the fusing of the powder in eachlayer or on one particular layer, an additional layer of powder isdispensed, and the process repeated, with fusion taking place betweenthe current layer and the previously laid layers until the article iscomplete. Detailed descriptions of the selective laser sinteringtechnology may be found in U.S. Pat. Nos. 4,863,538, 5,017,753,5,076,869 and 4,944,817. Quasi-porous structures have also beendeveloped in the form of regular and irregular lattice arrangements inwhich individual elements (column and connecting cross-members) areconstructed singularly from a pre-defined computer-aided design model ofthe external geometry and lattice structure. The selective laserremelting and sintering technologies have enabled the direct manufactureof solid or dense three-dimensional articles of high resolution anddimensional accuracy from a variety of materials including wax, metalpowders with binders, polycarbonate, nylon, other plastics and compositematerials, such as polymer-coated metals and ceramics.

The field of the rapid prototyping of parts has, in recent years, madelarge improvements in broadening high strain, high density, parts foruse in the design and pilot production of many useful articles,including metal parts. These advances have permitted the selective laserremelting and sintering processes to now also be used in fabricatingprototype tooling for injection molding, with expected tool life inaccess of ten thousand mold cycles. The technologies have also beenapplied to the direct fabrication of articles, such as molds, from metalpowders without a binder. Examples of metal powder reportedly used insuch direct fabrication include two-phase metal powders of thecopper-tins, copper-solder (the solder being 70% led and 30% tin), andbronze-nickel systems. The metal articles formed in these ways have beenquite dense, for example, having densities of up to 70% to 80% of fullydense (prior to any infiltration). Prior applications of this technologyhave strived to increase the density of the metal structures formed bythe remelting or sintering processes. The field of rapid prototyping ofparts has focused on providing high strength, high density, parts foruse and design in production of many useful articles, including metalparts.

However, while the field of rapid prototyping has focused on increasingdensity of such three-dimensional structures, the field has not focusedits attention on reducing the density of three-dimensional structures.Consequently, applications where porous and partially porous metallicstructures, and more particularly metal porous structures withinterconnected porosity, are advantageous for use have been largelyignored. The present invention is equally adapted for building porousstructure having a high density or a low density. It is an object ofthis invention to use a laser and powder metal to form pores instructures in which pores are irregular in size and have a controlledtotal porosity. It is a further object to produce porous tissue ingrowth surfaces with interconnected porosity with uniform pores andporosity.

SUMMARY OF THE INVENTION

The present invention relates to a method for producing athree-dimensional porous structure particularly for use with tissueingrowth. In one embodiment of the present invention, a layer ofmetallic powder is deposited onto a substrate or a build platform.Preferred metals for the powder include titanium, titanium alloys,stainless steel, cobalt chrome alloys, tantalum or niobium. A laser beamwith predetermined settings scans the powder layer causing the powder topreferentially remelt and consequently solidify with a decreaseddensity, resulting from an increase in porosity as compared to a solidmetal. The range of the laser's power may be between 5 W and 1000 W.After the first layer of powder has been completed, successive offsetlayering and remelting are continued until the porous part has beensuccessfully completed. In this embodiment, the benefit of the partformed is that that decreased density increases porosity thus enablingthe part to be used for, among other things, tissue ingrowth.

In a second embodiment, the first layer of metallic powder is depositedonto a solid base or core and fused thereto. Preferred metals used forthe core include titanium, titanium alloys, stainless steel, cobaltchrome alloys, tantalum and niobium. Successive powder layers of thesame or different materials are once again added in a layer-by-layerfashion until the part is completed. This embodiment has the desiredeffect of providing a structure in which the porosity may be increasedas the structure is built, resulting in a graded profile in which themechanical properties will also be reduced outwards from the core. Thiswill allow the formed part to be used for, among other things, medicalimplants and prosthesis, but yet still include a surface for tissueingrowth.

The method of producing a three-dimensional porous tissue ingrowthstructure may include depositing a first layer of a powder made from ametal selected from the group consisting of titanium, titanium alloys,stainless steel, cobalt chrome alloys, tantalum and niobium, onto asubstrate. Followed by scanning a laser beam at least once over thefirst layer of powder. The laser beam having a power (P) in Joule perseconds with a scanning speed (v) in millimeters per second with a rangebetween 80 and 400 mms. and a beam overlap (b) in millimeters of between50% and −1200%. Such that the number calculated by the formula P/(b×v)lies between the range 0.3-8 J/mm².

At least one additional layer of powder is deposited and then the laserscanning steps for each successive layer are repeated until a desiredweb height is reached. In a second embodiment, during the step ofrepeating the laser scanning steps, at least one laser scan is carriedout angled relative to another laser scan in order to develop aninterconnecting or non-interconnecting porosity.

The thickness of the first layer and said successive layers of powder isbetween 5 μm-2000 μm. The laser can be applied either continuously or ina pulse manner, with the frequency of the pulse being in the range ofapproximately 1 KHz to 50 KHz. Preferably, the method is carried outunder an inert atmosphere, more preferably specifically an Argon inertatmosphere.

In order to achieve a greater mechanical strength between the base orcore and the first layer of powder a third metal may be used to act asan intermediate. The third metal would act as a bond coat between thecore and first layer of powder. Additionally the core may be integralwith the resultant porous ingrowth structure and impart additionalphysical properties to the overall construct. The core may also bedetachable from the resultant porous surface buildup.

It is the object of the present invention to provide a method offabricating porous and partially porous metallic structures with a knownporosity for use in particularly but not exclusively hard or soft tissueinterlock structures or medical prosthesis.

These and other objects are accomplished by a process of fabricating anarticle in which laser-directed techniques are used to produce a porousthree-dimensional structure with interconnected porosity andpredetermined pore density, pore size and pore-size distribution. Thearticle is fabricated, in the example of remelting, by using a laser andvarying either the power of the laser, the layer thickness of thepowder, laser beam diameter, scanning speed of the laser or overlap ofthe beam. In fabricating a three-dimensional structure, the powder canbe either applied to a solid base or not. The article is formed inlayer-wise fashion until completion.

The present invention provides a method for building various structuresand surfaces but specifically medical implants. The structures are builtin a layer-by-layer fashion with individual layers including portions ofpredetermined unit cells.

In one embodiment of the present invention, a layer of metal powder isdeposited on a substrate. The substrate may be a work platform or abase, with the base or core being provided to possibly be an integralpart of the finished product. After an individual layer of powder isdeposited a scanning process may be preformed to selectively melt thepowder to form portions of a plurality of predetermined unit cells. Thescanning process includes scanning a laser beam onto the metal powder.

As successive layers are deposited and scanned a structure is built formone end to an opposite end. The structure includes a plurality ofpredetermined unit cells. The unit cells provide the structure withinterconnecting pores as well as porosity. The size of the pores andporosity as well as other factors may all be predetermined.

In one preferred embodiment the size of the pores of the porosity of thebuilt structure are specifically chosen to provide the structure withcharacteristics similar to medical implants.

In one aspect of the present invention disclosed is a method ofproducing a three-dimensional porous tissue in-growth structure. Themethod preferably includes depositing a first layer of a powder madefrom a metal selected from the group consisting of titanium, titaniumalloys, stainless steel, cobalt chrome alloys, tantalum and niobium ontoa substrate. The layer of powder is than scanned using a laser beam. Thelaser beam has a power, and scans the powder layer for a period of timewith a point distance. The power of the laser beam is preferably withinthe range of 5 to 1000 watts although the present invention may beadapted for different power ranges. Additionally, in a preferredembodiment, the exposure time is in a range between 100 μsec to 1000μsec. The laser beam scans the powder layer to form a portion of aplurality of predetermined unit cells. The predetermined unit cellsinclude struts having cross-sectional dimensions. The cross-section ofthe struts may be any regular of irregular shape. A few such examplesinclude circular, rectangular, cubic cross-sections or the like.

In one preferred embodiment of the present invention the laser power is90.5 W, the exposure time is 1000 μsec and the point distance is 90 μm.

The method also preferably includes depositing at least one additionallayer of the powder onto the first layer and repeating the step ofscanning the additional layers with a laser beam for at least one of thedeposited layers in order to continuing forming the predetermined unitcells.

The predetermined unit cells make take the shape of most regular orirregular structure. For example, the unit cells may be in the shape ofa tetrahedron, dodecahedron or octahedron as well as other symmetricalstructures. As mentioned, the unit cells may not have such uniformityand have an irregular shape. The unit cells may also be truncated, whichincludes eliminating some of the struts, which form a unit cell.Truncated unit cells located at the exterior surface of a built productprovide a barbed effect to the product.

In a preferred embodiment of the present invention, the layers of metalpowder have a thickness between 5 μm to 2000 μm.

The present invention may also include predetermining a porosity rangefor at least one deposited powder layer and scanning the layer in amanner to provide the deposited layer with porosity within thepredetermined porosity range.

In one aspect of the present invention, the substrate may include abase, core, work platform or the like. As with the layer of powder, themetal selected to form the base or core may be selected from the groupconsisting of titanium, titanium alloys, stainless steel, cobalt chromealloys, tantalum and niobium. Portions of the powder layers may be fusedand or sintered to the base or core. The base or core may either beseparated from the finished built product or may be an integral part ofthe finished product. If the base or core is an integral part of thefinished product it may impart additional physical properties to theoverall construct. The base or core may be constructed using the presentinvention.

In one aspect of the present invention a solid or semi-pervious layermay be placed between the substrate and the first deposited powderlayer.

In another aspect of the present invention during the at least one ofthe steps of the scanning process, a plurality of satellites may beformed on portions of the predetermined unit cells. The satellites mayremain attached to the predetermined unit cells so as to affect theporosity of the structure. In an alternate embodiment, the satellitesmay be removed. One way to remove the satellites is by an acid etchingprocess. The acid etching process may be conducted not only to removesome of all of the satellites but also to alter the cross-sectionaldimensions of various struts forming the predetermined unit cells.

In another aspect of the present invention, a plurality of struts mayintersect at an intersection point. Either prior to completion of aftercompletion of the finished structure, various intersection points may besintered. In one reason for sintering the intersection points is toeliminate any unmelted metal powder spots.

In a preferred aspect of the present invention, the laser beam may beadjusted to modify the length and/or cross-section of various struts.Additionally, at least some of the unit cells may be deformed so as todrape over the substrate. Laser beam compensation may also be employed.Some of the struts of the unit cells may overlap struts of other unitcells. This aspect also enables the adjusting of the porosity throughoutthe completed structure.

At least some of the predetermined unit cells may be coated withunmelted metal particles.

In one aspect of the present invention the metal powder layers aredeposited and scanned in order to form a medical implant. The medicalimplant preferably having porosity within a predetermined range. Themedical implant may include an acetabular cup, acetabular shell, a kneeimplant, femoral or hip implant or the like. The constructed medicalimplant may have a porosity, which promotes bone in-growth and/orprovides the medical implant with soft tissue characteristics.

The medical implants, as well as other constructed structures, may beprovided with an attaching mechanism for anchoring or at least morefirmly attaching the medical implant to another element. One suchexample is an acetabular shell being provided with a rim to snap-fit toan acetabular cup.

In another aspect of the invention, the structure may be subjected to ahot isostatic pressing.

In one preferred embodiment of the present invention, the method ofproducing a three-dimensional construct includes loading a file of acomponent into an engineering design package. The component is scaleddown in the file from its original size. A Boolean operation is nextperformed to subtract the scaled down component from the originalcomponent. This creates a jacket. The jacket can than be processed usinga bespoke application that populates the jacket with a repeating opencellular structure.

The open cellular structure is than sliced using the bespoke applicationto a predetermine thickness.

The main body of the file component jacket is loaded into a userinterface program and the jacket is sliced into layers having apredetermined thickness. Hatching is than applied to the file componentjacket as required to build a construct and the jacket is merged withthe open cellular lattice structure. Once a representation has beenobtained the depositing and scanning steps of the present invention maybe conducted to build the final product.

BRIEF DESCRIPTION OF THE DRAWINGS

Methods of forming the porous surface of the present invention can beperformed in many ways and some embodiments will now be described by wayof example and with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic illustration of the apparatus used to make testsamples according to the processes of the present invention;

FIG. 2 is a photographic image showing an array of samples produced bythe processes as performed by the apparatus of FIG. 1;

FIG. 3 is a table showing a series of parameters used for the samples ofFIG. 2;

FIGS. 4A to 10F are scanning electron microscope images of the surfacestructure of various samples made by the method according to theinvention;

FIG. 11 is a scanning electron microscope micrograph taken from a porousTi sintered structure;

FIG. 12 is an optical image of a section through a sample showing themicrostructure;

FIG. 13 is an image detailing surface structures;

FIGS. 14A-15B are non-contact surface profilimetry images detailing planviews of the samples; and

FIGS. 16A-25 are scanning electron microscope micrographs produced priorto multi-layer builds shown in FIGS. 7A-8E.

FIG. 26 indicates the metallography and spectra of a typical bond coatstructure.

FIG. 27 shows the effect of line spacing on pore size.

FIG. 28A-28F are examples of typical waffle structures.

FIG. 29 is a trabecular bone-type structure constructed from a micro CTscan.

FIG. 30 shows typical freestanding structures.

FIG. 31 shows a freestanding structure built using the preferredscanning strategy.

FIG. 32A illustrates one embodiment of a unit cell of the presentinvention;

FIG. 32B illustrates an alternate embodiment of a unit cell of thepresent invention.

FIG. 32C illustrates a lattice structure formed using a plurality ofunit cells illustrated in FIG. 32BB;

FIG. 33 illustrates lattice structures with and without laser beamcompensation formed using the unit cells illustrated in FIG. 32B;

FIG. 34A illustrates an alternate embodiment of a unit cell of thepresent invention;

FIG. 34B illustrates a lattice structure formed using a plurality ofunit cells illustrated in FIG. 34A;

FIG. 35 illustrates lattice structures formed with and without laserbeam compensation;

FIG. 36A illustrates an alternate embodiment of a unit cell of thepresent invention;

FIG. 36B illustrates a lattice structure formed using a plurality of theunit cells illustrated in FIG. 36A;

FIGS. 37A and 37B illustrate actual lattice structures formed using aplurality of unit cells represented in FIG. 36A;

FIG. 38A illustrates an additional embodiment of a unit cell of thepresent invention;

FIG. 38B illustrates a lattice structure created using a plurality ofunit cells illustrated in FIG. 38A;

FIG. 39A illustrates lattice structures created using unit cellsillustrated in FIG. 38A with varying exposure time;

FIG. 39B illustrates lattice structures created using unit cellsillustrated in FIG. 32A with varying exposure time;

FIG. 39C illustrates a side view of an embodiment of FIG. 39A;

FIG. 39D illustrates a side view of a lattice structure illustrated inFIG. 39B;

FIG. 40 is a representation of a lattice structure created using aplurality of the unit cells illustrated in FIG. 38A with randomperturbation;

FIG. 41 illustrates graduation of a solid to a lattice build;

FIG. 42 illustrates a graduation from one lattice density to another;

FIG. 43A illustrates a femoral hip component;

FIG. 43B illustrates an exploded view of FIG. 43A;

FIG. 44 illustrates the component of FIG. 43A with a reduced sizedfemoral attachment;

FIG. 45 illustrates a “jacket” created by the subtraction of theembodiment of FIG. 44 from the embodiment of FIG. 43A;

FIG. 46A illustrates one embodiment of a single unit cell for use in anopen cellular lattice structure;

FIG. 46B illustrates an open cellular lattice structure;

FIG. 47 illustrates the embodiment illustrated in FIG. 46B merged withthe embodiment illustrated in FIG. 44;

FIGS. 48A and 48B illustrate one embodiment of a finished product;

FIGS. 49A-49C illustrate an alternate embodiment of a finished product;

FIGS. 50A and 50B illustrate an alternate embodiment of a finishedproduct;

FIGS. 51A-51C illustrate an alternate embodiment of a finished product;

FIGS. 52A and 52B illustrate an alternate embodiment of a finishedproduct;

FIG. 53 illustrates an alternate embodiment of a finished product;

FIG. 54 illustrates an alternate embodiment of a finished product;

FIGS. 55A and 55B illustrate an apparatus used in conjunction with thepresent invention;

FIG. 56 illustrates a zoomed-in view of the embodiment illustrated FIG.55B;

FIG. 57 illustrates a zoomed-in view of the apparatus illustrated inFIG. 55B, further along in the process;

FIG. 58 illustrates a zoomed-in view of the apparatus illustrated inFIG. 55B, further along in the process;

FIGS. 59A and 59B illustrate porous surface coatings being applied to asubstrate;

FIGS. 60A and 60B illustrate one embodiment of a representation of afinished product;

FIGS. 61A and 61B illustrate one embodiment of a finished productcreated using the present invention;

FIGS. 62A to 62D illustrate one embodiment of a finished product createdusing the present invention;

FIG. 63 illustrates a titanium lattice structure with hierarchicalsurface coating of sintered titanium satellites; and

FIGS. 64-71 illustrate the change occurring to the embodimentillustrated in FIG. 63, while the lattice is exposed to a laser atincreasing time periods.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of forming porous andpartially porous metallic structures which are particularly but notexclusively applicable for use in hard or soft tissue interlockstructures for medical implants and prosthesis. The method makes use oflaser technology by employing a variety of scanning strategies. Typicalmetal and metal alloys employed include stainless steel, cobalt chromiumalloys, titanium and its alloys, tantalum and niobium, all of which havebeen used in medical device applications. The present invention can beused for such medical device applications where bone and soft tissueinterlock with a component is required, or where a controlled structureis required to more closely match the mechanical properties of thedevice with surrounding tissue. Additionally, the present invention maybe employed to enhance the biocompatibility of a porous structure withanimal tissue. With these advantages in mind, a structure may be createdusing specific dimensions required to accommodate a particular patient.

One particular intention of the present invention is to produce athree-dimensional structure using a laser remelting process, forexample, for building structures with or without a solid base or core.When applied to an orthopedic prosthesis, the three-dimensionalstructure could be used to provide a porous outer layer to form a bonein-growth structure. Alternatively, the porous structure, when appliedto a core, could be used to form a prosthesis with a defined stiffnessto both fulfill the requirement of a modulus match with surroundingtissue and provide interconnected porosity for tissue interlock. Afurther use could be to form an all-porous structure with grade poresize to interact with more than one type of tissue. Again, the processcan be used to build on a solid base or core with an outer poroussurface, the porosity of which is constant or which varies. The base orcore materials to which the process is applied may be either titaniumand its alloys, stainless steel, cobalt chrome alloys, tantalum orniobium as well as any other suitable material. The preferred surfacecoatings are titanium, cobalt chrome and tantalum but both stainlesssteel and niobium can also be used as well as any other suitablematerial. Fully porous structures may be built from any of the materialstested, with the preferred material being titanium. One intention of thepresent invention is to produce a method which can be exploited on acommercial basis for the production of, for example, bone interlocksurfaces on a device although it has many other uses.

According to the present invention, a method of forming athree-dimensional structure includes building the shape by laser meltingpowdered titanium and titanium alloys, stainless steel, cobalt chromealloys, tantalum or niobium using a continuous or pulsed laser beam.Individual layers of metal are scanned using a laser. The laser may be acontinuous wave or pulsed laser beam. Each layer or portion of a layeris scanned to create a portion of a plurality of predetermined unitcells, as will be described below. Successive layers are deposited ontoprevious layers and also may be scanned. The scanning and depositing ofsuccessive layers continues the building process of the predeterminedunit cells. As disclosed herein, by continuing the building processrefers not only to a continuation of a unit cell from a previous layerbut also a beginning of a new unit cell as well as the completion of aunit cell.

The method can be performed so that the structure is porous and ifdesired, the pores can be interconnecting to provide an interconnectedporosity.

If desired, the method can include using a base or core of cobalt chromealloy, titanium or alloy, stainless steel, niobium and tantalum, onwhich to build a porous layer of any one of the aforementioned metalsand alloys by laser melting using a continuous or pulsed laser beam.Thus, a mixture of desired mixed materials may be employed.

The method can be applied to an existing article made from cobaltchrome, titanium or titanium alloys, stainless steel, tantalum orniobium, such as an orthopedic implant, to produce a porous outer layerfrom any of the aforementioned metals or alloys to provide a bonein-growth structure.

Preferably, prior to the deposition of any powder onto a substrate, acleaning operation to ensure a contaminant-free surface may be employed.Typically, this process may include a solvent wash followed by acleaning scan of the laser beam without the presence of particles.

In order to increase the mechanical bond between a substrate i.e., coreor base, and a first layer of deposited powder a coating process may beemployed. The coating process includes applying a third metal directlyto the substrate, which has a higher bond strength to the substrate thendoes the first layer of powder. This process is particularly useful whenthe substrate and first powder layer are of different materials. Theprocess of coating the substrate may be accomplished using knownprocesses including laser deposition, plasma coating, cold gas dynamicspraying or similar techniques. One example of the coating processincludes using either niobium or tantalum as an interface between acobalt chrome alloy substrate and a first layer of titanium powder.

The present invention can include a laser melting process, whichprecludes the requirement for subsequent heat treatment of thestructure, thereby preserving the initial mechanical properties of thecore or base metal. The equipment used for the manufacture of such adevice could be one of many currently available including the MCPRealiszer, the EOS M270, Trumpf Trumaform 250, the Arcam EBM S12 and thelike. The laser may also be a custom produced laboratory device.

The method may be applied to produce an all-porous structure using anyof the aforementioned metal or metal alloys. Such structures can be usedas finished or final products, further processed to form a useful devicefor bone or soft tissue in-growth, or used to serve some other functionsuch as that of a lattice to carry cells, for example.

The pore density, pore size and pore size distribution can be controlledfrom one location on the structure to another. It is important to notethat successive powder layers can differ in porosity by varying factorsused for laser scanning powder layers. As for example, a first layer ofpowder is placed and subsequently scanned. Next a second layer of powderis placed and scanned. In order to control porosity the second scan maybe angled relative to the first scan. Additionally, the angling of thescanning as compared to previous and post scans may be maneuvered andchanged many times during the process of building a porous structure. Ifa structure was built without alternating the angling of any subsequentscans you would produce a structure having a plurality of walls ratherthan one with an interconnecting or non-interconnecting porosity.

In one such method, the laser melting process includes scanning thelaser beam onto the powder in parallel scan lines with a beam overlapi.e., scan spacing, followed by similar additional scans or subsequentscans at 90°. The type of scan chosen may depend on the initial layerthickness as well as the web height required. Web height refers to theheight of a single stage of the porous structure. The web height may beincreased by deposited additional layers of powder of a structure andscanning the laser at the same angle of the previous scan.

Further, the additional scan lines may be at any angle to the firstscan, to form a structure with the formation of a defined porosity,which may be regular or random. The scan device may be programmed toproceed in a random generated manner to produce an irregular porousconstruct but with a defined level of porosity. Furthermore, the scancan be pre-programmed using digitized images of various structures, suchas a trabecular bone, to produce a similar structure. Contrastingly, thescan may be pre-programmed using the inverse of digitized images, suchas the inverse of a digitized trabecular bone to produce trabecularshaped voids. Many other scanning strategies are possible, such as awaffle scan, all of which can have interconnecting porosity if required.

The beam overlap or layer overlap may be achieved by rotation of thelaser beam, the part being produced, or a combination of both.

A first method according to the present invention is intended to producea porous structure for bone in-growth on the outer surface layer of aprosthesis. To produce a porous surface structure, the nature of thematerial formed as a result of laser melting of powdered beads isprincipally dependent on the thermal profile involved (heating rate,soaking time, cooling rate); the condition of the raw material (size andsize distribution of powder particles); atmospheric conditions(reducing, inert or oxidizing chamber gas)In some instances, the natureof the material formed may be further a result of accurate control ofthe deposited layer thickness.

There have been a number of studies to determine the optimum porestructure for maximization of bone in-growth on prostheses. The generalfindings suggest that optimum porosity is between approximately 20% and40%, and aim to mid value with a mean volume percent of voids of about70%. The preferred pore structure is interconnected, with a minimum poresize between about 80 μm and 100 μm and a maximum pore size between 80μm and 800 μm. The structured thickness for in-growth is 1.4-1.6 mm, butcan be larger or smaller depending on the application. As for example,it may be necessary to produce even smaller pore sizes for other typesof tissue interaction or specific cellular interaction.

The first phase of development of the present invention involved aninvestigation, designed to characterize the material transformationprocess and to identify the optimum parameters for processing usingthree substrate materials CoCr and Ti stainless steel alloys, with fivepowder types Ti, CoCr, Ta and Nb, stainless steel.

The initial Direct Laser Remelting trials explored a comprehensive rangeof process parameters during the production of a number of coated basesubstrates. Results from this task were evaluated using laser scanningand white light interferometry in order to define the range of processparameters that produced the optimum pore structure.

Referring to FIG. 1, there is shown the apparatus used to carry out themethod which comprises an Nd; YAG industrial laser 1 manufactured byRofin Sinar Lasers, in Hamburg, Germany, integrated to an RSG1014analogue galvo-scanning head 2 providing a maximum scan speed of 500mm/s. The laser beam 3 is directed into an atmospherically controlledchamber 4, which consists of two computer-controlled platforms forpowder delivery and part building. The powder is delivered from avariable capacity chamber 5 into the chamber 4 and is transported by aroller 6 to a build platform 7 above a variable capacity build chamber8. In the embodiment shown in FIG. 1, the build and delivery systemparameters are optimized for an even 100 μm coating of powder to bedeposited for every build layer. The metals chosen as surface materialsare all difficult to process due to their affinity for oxygen. Cr and Tiare easily oxidized when processed by laser in oxygen-containingatmosphere, their oxide products have high melting points and poorflowability. For this reason, and to prevent the formation of otherundesirable phases, the methods were carried out under an Argon inertatmosphere in chamber 8. Pressure remained at or below atmosphericpressure during the entire application.

The build chamber 8 illustrated in FIG. 1 and method of layeringdescribed above is suitable for test specimens and constructs such asthree-dimensional freestanding structures. However, in order to build onto an existing device, such as acetabular metal shells, hip and kneefemoral components, knee tibial components and other such devices,considerable changes to the powder laying technique would need to beapplied.

Preliminary experiments were performed on CoCr alloy to determine theefficacy of in-situ laser cleaning of the substrate. Typical processingconditions were: Laser power of 82 W, pulse frequency of 30 KHz, and alaser scan speed of 160 mm/sec.

Preliminary experiments were performed on CoCr to assess the environmentconditions within the chamber. In these examples, Co212-e Cobalt Chromealloy was used. The CoCr was configured into square structures, calledcoupons. Arrays of CoCr coupons were built onto a stainless steelsubstrate. The Co212-e Cobalt Chrome alloy had a particle sizedistribution of 90<22 um, i.e., 90% of the particles are less than 22μm, the composition of which is shown in the table below.

TABLE 1 Composition of Co212-e CoCr alloy Element Cr Mo Si Fe Mn Ni N CCo Wt % 27.1 5.9 0.84 0.55 0.21 0.20 0.16 0.050 Balance

An array of nine sample coupons were produced as shown in FIG. 2, withthe process of Table 2, using a maximum laser power of 78 watts (W) andlaser scanning speed for each coupon varying between 100-260 mms⁻¹. Ofcourse a higher laser power may be employed; however, a higher laserpower would also necessitate increasing the speed of the laser scanspeed in order to produce the desired melting of the powder layer. Asimple linear x-direction scan was used on each of the coupons. Thisallowed the processing parameter, beam overlap, to be used to controlthe space between successive scan lines. That is, with a 100 μm laserspot size, an overlap of −200% produces a 100 μm gap between scans.Although the acceptable range for the beam overlap is given at +50% to−1200% it should be duly noted that the negative number only refers tothe fact the there is a gap as opposed to a beam overlap betweensuccessive scans. For instance a beam overlap of zero refers to the factthat successive scans on the same layer of powder border each other. Ifthe beam overlap was 5% then 5% of the first scan is overlapped by thesecond scan. When computing the Andrew number the absolute value of thebeam overlap is used. The complete set of process parameters used isshown in Table 2 below.

TABLE 2 Process parameters Power Layer Beam Scanning Overlap WattsThickness Diameter Speed Atmos- No. of (% of line (W) (μm) (μm) (mms⁻¹)phere Layers width) 78 100 100 100-260 No 16 25,50,-500

The incremental changes in scanning speed and the size of the speedrange were modified as the experiments progressed. To begin with, alarge range of speeds was used to provide an initial indication of thematerial's performance and the propensity to melt. As the experimentsprogressed, the range was reduced to more closely define the processwindow. Speed and beam overlap variations were used to modify thespecific energy density being applied to the powder bed and change thecharacteristics of the final structure. The complete series ofparameters are given in FIG. 3, the parameters sets used for thedefinitive samples are shaded in gray.

CoCr was the first of four powders to be examined and, therefore, a widerange of process parameters was used. In each case, laser power and thepulse repetition rate were kept constant, i.e., continuous laser pulse,to allow the two remaining parameters to be compared. Layer thicknesswas maintained at 100 μm throughout all the experiments described here.Layer thickness can, however, vary between 5 μm to 2000 μm.

On completion of the initial series of experiments using CoCr powder on2.5 mm thick stainless steel substrates, basic optical analysis wasconducted of the surface of the coupons to ascertain the size of thepores and degree of porosity being obtained. Once a desired pore sizewas obtained and the coupons had suitable cohesion, the two experimentsclosest to the optimum desired pore size were repeated using first CoCrand then Ti substrates. The same structure could be obtained by otherparameters.

Following the conclusion of the CoCr experiments, the remaining threepowders; Niobium, Tantalum and Titanium were investigated in turn. Theprocedure followed a simple course although fewer parameter sets wereexplored as the higher melting points of these materials forced thereduction in speeds compared to CoCr powder.

For Niobium, the particle size description was 80%<75 μm at a purity of99.85%. Due to its higher melting temperature compared to that of CoCr(Nb being at about 2468° C., and CoCr being at about 1383° C.), thelaser parameters used included a reduced scanning speed range andincreased beam overlap providing increased specific energy density atthe powder bed. In addition, the pulse repetition rate was varied from20 kHz to 50 kHz.

On completion of a small number (four in total) of preliminaryexperiments of Nb on stainless steel substrate, the experiment with themost ideal parameters was repeated on both the CoCr and Ti substrates.

The Tantalum used in this study had a particular size distribution of80%<75 μm with a purity of 99.85%. Ta has a melting point of about 2996°C. and was processed using the same laser parameters as Nb. Nowconfident of the atmospheric inertness, the Ta powder was melteddirectly onto the CoCr and Ti substrates.

Bio-medical alloys of Titanium were not readily available in powder formand so pure Ti was chosen. The particle size distribution for the Tipowder was 80%<45 μm with a purity of 99.58%. The same parameters usedfor Nb and Ta were also used for the Ti powder. Ti has a lower meltingpoint than Ta or Nb, Ti being at about 1660° C., but has a higherthermal conductivity than Ta or Nb. This implies that although thepowder should require less energy before melting, the improved heattransfer means a larger portion of the energy is conducted away from themelt pool.

Following the completion of samples with all four powders on therequired substrates, surface analysis was conducted using opticalanalysis and a scanning electron microscope to obtain images of theresultant pores. Porosity was calculated using a simple image processingtechnique involving the setting of contrast thresholds and pixelcounting. While this technique is not the most accurate method, itallows the rapid analysis of small samples produced. Techniques such asXylene impregnation would yield more accurate results but they are timeconsuming and require larger samples than those produced here.

Following an extended series of experimentation, two sets of laserprocessing parameters were selected for the laser melting of CoCrpowder. From analysis of the stainless steel substrates, it was seenthat a large portion of the results fell within the pore size requiredfor these materials, stated as being in the range of 80 μm to 400 μm.

Optical analysis of the surface structure of each of the couponsproduced with CoCr on CoCr and Ti alloy substrates were initially viewedbut due to problems with the depth of field associated with an opticalmicroscope, little information could be extracted. In addition to thecoupons that were produced to satisfy the project requirements, twoexperiments were conducted using a relatively large negative beamoverlap of −250 and −500%. Optical images of the coupon's surface and insection are shown in FIG. 4. These were not the definitive parameterschosen for the final arrays on CoCr and Ti alloy substrates as the poresize exceeds the required 80 μm to 400 μm. They are shown here todisplay what the Direct Laser Remelting process can produce when anexcessive beam overlap is used.

To provide a clearer indication of the pore size and pore density, theoptical analysis was repeated using images obtained from the scanningelectron microscope. FIG. 5 is an image of two coupons produced from aCoCr array on Ti alloy substrates. This array was chosen because it bestsatisfied the requirements of this exercise. The parameters were: laserpower of 82 W continuous wave (cw); 25% beam overlap; scanning speedvaried from 100 mms-¹ to 260 mms-¹ in 20 mm-¹ increments; the images ofthe coupons shown here, taken from this array, were produced withscanning speeds of 180 mms⁻¹ to 200 mms⁻¹. The surface is comprised offused pathways that develop a network of interconnected pores. Thisstructure continues throughout the layer until the interface is reached.The interface is characterized by a patchwork of fusion bonds. Thesebond sites are responsible for securing the interconnected surfacestructure to the baseplate. The macroscopic structure is covered withunmelted powder particles that appear to be loosely attached. Inaddition, there are larger resolidified globules that may have limitedbonding to the surface.

FIGS. 6 and 7 are the scanning electron microscope images produced fromthe Nb and Ta coupons on Ti alloy substrates. Specifically, FIGS. 6A to6E are scanning election microscope images of the surface structure ofNb on Ti alloy substrates, produced with a laser power of 82 W cw, −40%beam overlap. The scanning speeds used were: 160 mms⁻¹ for FIG. 6A, 190mms⁻¹ for FIG. 6A, 200 mms⁻¹ for FIG. 6C, 210 mms⁻¹ for FIG. 6D and 240mms⁻¹ for FIG. 6E, respectively.

FIGS. 7A to 7C are scanning election microscope images of the surfacestructure of Ta on Ti alloy substrates produced using the sameparameters used in the Nb or Ti alloy substrates except: FIG. 7A wasproduced with a scanning speed of 160 mms⁻¹; FIG. 7B's speed was 200mms⁻¹ and FIG. 7C's speed was 240 mms⁻¹, respectively. An increased beamoverlap was used here as Nb and Ta have high melting points, whichrequire a greater energy density. The surfaces once again exhibitsignificant levels of unmelted powder particles and loosely attachedresolidified beads that vary in size from a few microns to severalhundred microns. All samples were loosely brushed after completion andcleaned in an ultrasonic aqueous bath. It is possible that furthercleaning measures may reduce the fraction of loose particles.

FIGS. 8A to 8E are scanning electron microscope images taken from the Ticoupons on the CoCr alloy substrates. The laser processing parametersused were the same as those for the Nb and Ta powders, with once againonly the speed varying. The scanning speed was varied from 160 mms⁻¹(FIG. 8A, 170 mms⁻¹ (FIG. 8B), 200 mms⁻¹ (FIG. 8C); 230 mms⁻¹ (FIG. 8D)to 240 mms⁻¹ (FIG. 8E). The Ti coupon on CoCr samples, (FIGS. 8A to 8C)indicate very high density levels compared to the other examples. Theline-scans can be clearly seen, with good fusion between individualtracks, almost creating a complete surface layer. The surface begins tobreak up as the scanning speed is increased.

FIGS. 9A to 9E are scanning electron microscope images of surfacestructures of Ti on Ti alloy substrates produced with the sameparameters used in FIGS. 8A to 8E, respectively. It is unclear why Tishould wet so well on CoCr substrates. In comparison, Ti on Ti exhibitssimilar characteristic patterns as with Nb, Ta, and CoCr, specifically,an intricate network of interconnected pores.

Following the completion of the multi-layer coupons, a series of 20mm×20 mm structures were produced from Ti that utilized an X andY-direction “waffle” scanning format using the optimum Ti operatingparameters with the two scans being orthogonal to one another. Theintention behind these experiments was to demonstrate the ability of theDirect Laser Remelting process to produce parts with a controlledporosity, e.g. internal channels of dimensions equal to the requiredpore size, e.g. 80 μm to 400 μm. To do this, a relatively large beamoverlap of between −400% and −600% was used. Scanning electronmicroscope images of the surfaces of these structures are shown in FIGS.10A to 10F. The scanning speed, 160 mms⁻¹ and the laser power 72 W cwwere kept constant while the beam overlaps; −400% in FIGS. 10A and 10B;−500% in FIGS. 10C and 10D and −600% in FIGS. 10E and 10F, were variedaccordingly. Scanning electron microscope micrographs, taken from aporous Ti sintered structure provided by Stryker-Howmedica are shown forreference in FIG. 11.

To illustrate more clearly the interaction between thesubstrate/structure metallurgical interaction, the Ti on Ti substratewas sectioned, hot mounted and polished using a process of 1200 and 2500grade SiC, 6 μm diamond paste and 70/30 mixture of OPS and 30% H₂O₂. Thepolished sample was then etched with 100 ml H₂O, 5 ml NH.FHF and 2 cm³HCl for 30 seconds to bring out the microstructure. Optical images ofthis sample in section are shown in FIG. 12.

FIG. 13 is an image taken from a non-contact surface profilimentry toshow the surface structures obtained when using Ti, CoCr, Ta and Nb onTi substrates. Values for Ra, Rq and Rb roughness are also shown.

From the optical and scanning election microscope analysis conducted, itis apparent that the Direct Laser Remelting process is capable ofsatisfying the requirements for pore characteristics, concerning maximumand minimum pore size, interconnectivity and pore density. From theinitial visual analysis of the CoCr coupons, it was apparent from theseand other examples, that subtle variations in pore structure andcoverage could be controlled by scanning velocity and line spacing.

The key laser parameters varied for forming the three-dimensionalmetallic porous structures are: (a) Laser scanning speed (v.) in(mms⁻¹), which controls the rate at which the laser traverses the powderbed; (b) Laser power, P(W), which in conjunction with the laser spotsize controls the intensity of the laser beam. The spot size was keptconstant throughout the experiment; (c) Frequency, (Hz) or pulserepetition rate. This variable controls the number of laser pulses persecond. A lower frequency delivers a higher peak power and vice versa.

The line width can be related to the laser scanning speed and the laserpower to provide a measure of specific density, known as the “AndrewNumber”, where:

${An} = {\frac{P}{b \times v}\left( {J\text{/}{mm}^{- 2}} \right)}$Where P denotes the power of the laser, v is the laser scanning speedand b denotes beam width of the laser. The Andrew number is the basisfor the calculation of the present invention. The Andrew number may alsobe calculated by substituting the line separation (d) for beam width(b). The two methods of calculating the Andrew number will result indifferent values being obtained. When using line separation (d) as afactor only on track of fused powder is considered, whereas when usingthe beam width (b) as a factor, two tracks of fused powder areconsidered as well as the relative influence of one track to the next.For this reason we have chosen to concern ourselves with the Andrewnumber using scan spacing as a calculating factor. It can thus beappreciated, that the closer these tracks are together the greater theinfluence they have on one another.

Additionally, the laser power may be varied between 5 W and 1000 W.Utilizing lower power may be necessary for small and intricate parts butwould be economically inefficient for such coatings and structuresdescribed herein. It should be noted that the upper limit of laser poweris restricted because of the availability of current laser technology.However, if a laser was produced having a power in excess of 1000 W, thescanning speed of the laser could be increased in order that anacceptable Andrew number is achieved. A spot size having a range between5 um(fix) to 500 um(fix) is also possible. For the spot size to increasewhile still maintaining an acceptable Andrew number, either the laserpower must be increased or the scanning speed decreased.

The above formula gives an indication of how the physical parameters canvary the quantity of energy absorbed by the powder bed. That is, if themelted powder has limited cohesion, e.g. insufficient melting, theparameters can be varied to concentrate the energy supply to the powder.High Andrew numbers result in reduced pore coverage and an increase inpore size due to the effects of increased melt volume and flow. LowAndrew numbers result in low melt volume, high pore density and smallpores. Current satisfactory Andrew numbers are approximately 0.3 J/mm⁻²to 8 J/mm⁻² and are applicable to many alternative laser sources. It ispossible to use a higher powered laser with increased scanning speed andobtain an Andrew number within the working range stated above.

Line spacing or beam overlap can also be varied to allow for a gapbetween successive scan lines. It is, therefore, possible to heatselected areas. This gap would allow for a smaller or larger pore sizeto result. The best illustration of this is shown in FIGS. 4A to 4Cwhere a −500% beam overlap has been applied. FIGS. 4A to 4C are scanningelection microscope images of the surface structure of CoCr on stainlesssteel produced with a laser power of 82 W cw. FIG. 4A was produced witha laser scanning speed of 105 mms⁻¹ and FIG. 4B was produced with alaser scanning speed of 135 mms⁻¹. FIG. 4C is an image of the samestructure in FIG. 4B, in section. There is a significant self-orderingwithin the overall structure. Larger columnar structures are selectivelybuilt leaving large regions of unmelted powder. It is worth noting thatthese pillars are around 300 μm wide, over 1.6 mm tall and fuse wellwith the substrate, as seen in FIG. 4C. Further analysis shows that theuse of a hatched scanning format allows porosity to be more sufficientlycontrolled to allow the pore size to be directly controlled by the beamoverlap.

The use of an optical inspection method to determine this approximateporosity is appropriate given the sample size. This method, although notaccurate due to the filter selection process, can, if used carefully,provide an indication of porosity. An average porosity level of around25% was predicted. This porosity level falls within the range of thedesired porosity for bone in-growth structures. The mechanicalcharacteristics of the porous structures are determined by the extent ofporosity and the interconnecting webs. A balance of these variables isnecessary to achieve the mechanical properties required by the intendedapplication.

Increased fusion may, if required, be obtained by heating the substrate,powder or both prior to scanning. Such heating sources are commonlyincluded in standard selective laser sintering/melting machines topermit this operation.

Following trials on the titanium build on the cobalt chromium substrate,it was determined that the interface strength was insufficient to servethe intended application. Trials were made by providing a bond coat ofeither tantalum or niobium on the cobalt chromium substrate prior to thedeposition of the titanium layers to for the porous build. The typicalprotocol involved:

-   -   (i) Initial cleaning scan with a scan speed between 60 to 300        mm/sec, laser power 82 watts, frequency of 30 KHz, and a 50%        beam overlap.    -   (ii) Niobium or tantalum deposition with three layers of 50 μm        using a laser power of 82 watts, frequency 30 to 40 KHz, with a        laser speed of between 160 to 300 mm/sec. The beam overlap was        low at 50% to give good coverage.    -   (iii) A build of porous titanium was constructed using a laser        power of 82 watts, frequency between 0 (cw) and 40 KHz, scanning        speed of between 160 and 240 mm/sec, and beam overlap of −700%.        The strengths of the constructs are indicated in Table 3 with a        comparison of the values obtained without the base coat.

TABLE 3 TENSILE MAXIMUM STRENGTH SPECIMEN LOAD (kN) (MPa) FAILURE MODETi on CoCr 2.5 5   Interface Ti on CoCr 3.1 6.2 Interface 1 (Nb onCo-Cr) 13.0  26.18 65% adhesive, 35% bond interface 4 (Ti on Nb on  7.7615.62 Mostly bond coat interface Co-Cr) 5 (Ti on Nb on  9.24 18.53 20%adhesive, 40% bond Co-Cr) coat, 40% porous Ti 6 (Ti on Ta on 11.58 23.33Mostly adhesive with Co-Cr) discrete webbing weakness 8 (Ta on Co-Cr)13.93 27.92 60% adhesive, 40% bond interface 9 (Ti on Ta on  6.76 13.62100% bond interface Co-Cr)FIG. 26 shows the metallography of the structures with energy dispersivespectroscopy (EDS) revealing the relative metal positions within thebuild.

A typical waffle build of titanium on a titanium substrate wasconstructed as a way of regulating the porous structure. Scanningsequences of 0° 0°0°, 90° 90° 90°, 45° 45° 45°, 135°,135°, 135°, oflayer thickness 0.1 mm were developed to form a waffle. Three layers ofeach were necessary to obtain sufficient web thickness in the “z”direction to give a structure of adequate strength. Typical parametersemployed were: Laser power was 82 watts, operating frequency between 0(cw) and 40 KHz, scan speed of between 160 and 240 mm/sec with a beamoverlap of −700%. FIG. 27 gives an indication of the effect of linespacing and pore size. FIG. 28A shows typical examples of the wafflestructure. The magnification level changes from 10, 20, 30, 70 and 150times normal viewing as one moves respectively from FIG. B to F. FIG.28A more specifically shows Ti powder on a Ti substrate with acontrolled porosity by varying line spacing, i.e., beam overlap.

Trabecular structures of titanium on a titanium substrate wereconstructed as a way of randomising the porous structures. An STL(sterolithography) file representing trabecular structure was producedfrom a micro CT scan of trabecular bone. This file was sliced and theslice data sent digitally to the scanning control. This allowed thelayer-by-layer building of a metallic facsimile to be realised. FIG. 29shows a cross-sectional view of such a construct.

A method for making lattice-type constructs was referred to in therelevant art. A typical example of this type of structure is shown inFIG. 30. The scanning strategy employed to form such a construct wasmentioned and such a strategy could be produced within the range ofAndrew numbers outlined. Table 4 shows an indication of scanningstrategies and their relationships to the Andrew number.

TABLE 4 Ti on Ta on CoCr Experimental Procedure. Initial TantalumCoating RELATIVE BUILD SCAN PARAMETER LAYER PLATFORM LAYER STRATEGY SETTHICKNESS POSITION ADDITIONAL Zero    0 Distance Between Roller & BuildPlatform 0 1^(st) layer 50 μm  −50 μm thickness set using feeler gaugesbut powder not laid in preperation for cleaning scan with no powder. 150% Beam P = 82 W Initial Overlap Qs = 30 kHz Cleaning Scan v = 60 mm/s(no powder) A_(n) = 27.333 J/mm² Circular profile. P = 82 W Powder laid5 concentric Qs = 40 kHz as usual circles, 0.1 mm V = 160 mm/s offset tonegate A_(n) = effects of ‘First 5.125 J/mm² Pulse’ 50% Beam P = 82 WScanned on Overlap Qs = 30 kHz same powder v = 300 mm/s layer as A_(n) =previous 5.467 J/mm² profile scan. 2 Circular profile. P = 82 W 50 μm−100 μm Powder laid 5 concentric Qs = 40 kHz as usual circles, 0.1 mm V= 160 mm/s offset to negate A_(n) = effects of ‘First 5.125 J/mm² Pulse’50% Beam P = 82 W Scanned on Overlap Qs = 30 kHz same powder v = 300mm/s layer as A_(n) = previous 5.467 J/mm² profile scan. 3 Circularprofile. P = 82 W 50 μm −150 μm Powder laid 5 concentric Qs = 40 kHz asusual circles, 0.1 mm V = 160 mm/s offset to negate A_(n) = effects of‘First 5.125 J/mm² Pulse’ 50% Beam P = 82 W Scanned on Overlap Qs = 30kHz same powder v = 300 mm/s layer as A_(n) = previous 5.467 J/mm²profile scan.

Final Titanium Coating RELATIVE BUILD SCAN PARAMETER LAYER PLATFORMLAYER STRATEGY SET THICKNESS POSITION ADDITIONAL 0 1^(st) layer −150 μmthickness set using feeler gauges but powder not laid in preperation forcleaning scan with no powder. 1 50% Beam P = 82 W  50 μm −200 μmCleaning Scan Overlap Qs = 30 kHz (No powder. v = 60 mm/s A_(n) = 27.3J/mm² Circular profile. P = 82 W Powder spread 5 concentric Qs = 40 kHzbut build circles, 0.1 mm V = 160 mm/s platform not offset to negateA_(n) = lowered. effects of ‘First 5.125 J/mm² Pulse’ 50% Beam P = 82 WScanned on Overlap Qs = 30 kHz same powder v = 300 mm/s layer as A_(n) =previous 5.467 J/mm² profile scan. 2 Circular profile. P = 82 W 100 μm−300 μm Powder laid 5 concentric Qs = 40 kHz as usual circles, 0.1 mm V= 160 mm/s offset to negate A_(n) = effects of ‘First 5.125 J/mm² Pulse’25% Beam P = 82 W Scanned on Overlap Qs = 30 kHz same powder v = 300mm/s layer as A_(n) = previous 3.644 J/mm² profile scan. 3 Circularprofile. P = 82 W 100 μm −400 μm Powder laid 5 concentric Qs = 40 kHz asusual circles, 0.1 mm V = 160 mm/s offset to negate A_(n) = effects of‘First 5.125 J/mm² Pulse’ 0% Beam P = 82 W Scanned on Overlap Qs = 30kHz same powder v = 300 mm/s layer as A_(n) = previous 2.733 J/mm²profile scan. 4 Waffle 0 and 90° P = 82 W  75 μm −475 μm Powder laid 700μm Qs = 0 Hz (cw) as usual linespacing v = 240 mm/s (−600% Beam A_(n) =overlap) 0.488 J/mm² 5 Waffle 0 and 90° P = 82 W  75 μm −550 μm Powderlaid 700 μm Qs = 0 Hz (cw) as usual linespacing v = 240 mm/s (−600% BeamA_(n) = overlap) 0.488 J/mm² 6 Waffle 0 and 90° P = 82 W  75 μm −625 μmPowder laid 700 μm Qs = 0 Hz (cw) as usual linespacing v = 240 mm/s(−600% Beam A_(n) = overlap) 0.488 J/mm² 7 Waffle 45 and 135° P = 82 W 75 μm −700 μm Powder laid 700 μm Qs = 0 Hz (cw) as usual linespacing v= 240 mm/s (−600% Beam A_(n) = overlap) 0.488 J/mm² 8 Waffle 45 and 135°P = 82 W  75 μm −775 μm Powder laid 700 μm Qs = 0 Hz (cw) as usuallinespacing v = 240 mm/s (−600% Beam A_(n) = overlap) 0.488 J/mm² 9Waffle 45 and 135° P = 82 W  75 μm −850 μm Powder laid 700 μm Qs = 0 Hz(cw) as usual linespacing v = 240 mm/s (−600% Beam A_(n) = overlap)0.488 J/mm²

Ti on Ti Experimental Procedure. Initial Titanium Coating RELATIVE BUILDSCAN PARAMETER LAYER PLATFORM LAYER STRATEGY SET THICKNESS POSITIONADDITIONAL Zero    0 Distance Between Roller & Build Platform 0 1^(st)layer 50 μm  −50 μm thickness set using feeler gauges but powder notlaid in preperation for cleaning scan with no powder. 1 50% Beam P = 82W Initial Overlap Qs = 30 kHz Cleaning Scan v = 60 mm/s (no powder)A_(n) = 27.333 J/mm² Circular profile. P = 82 W Powder laid 5 concentricQs = 40 kHz as usual circles, 0.1 mm V = 160 mm/s offset to negate A_(n)= effects of ‘First 5.125 J/mm² Pulse’ 50% Beam P = 82 W Scanned onOverlap Qs = 30 kHz same powder v = 300 m/s layer as A_(n) = previous5.467 J/mm² profile scan. 2 Circular profile. P = 82 W 50 μm −100 μmPowder laid 5 concentric Qs = 40 kHz as usual circles, 0.1 mm V = 160mm/s offset to negate A_(n) = effects of ‘First 5.125 J/mm² Pulse’ 50%Beam P = 82 W Scanned on Overlap Qs = 30 kHz same powder v = 300 mm/slayer as A_(n) = previous 5.467 J/mm² profile scan. 3 Circular profile.P = 82 W 50 μm −150 μm Powder laid 5 concentric Qs = 40 kHz as usualcircles, 0.1 mm V = 160 mm/s offset to negate A_(n) = effects of ‘First5.125 J/mm² Pulse’ 50% Beam P = 82 W Scanned on Overlap Qs = 30 kHz samepowder v = 300 mm/s layer as A_(n) = previous 5.467 J/mm² profile scan.

Final Titanium Coating RELATIVE BUILD SCAN PARAMETER LAYER PLATFORMLAYER STRATEGY SET THICKNESS POSITION ADDITIONAL 1 Circular profile. P =82 W 100 μm −250 μm Powder laid 5 concentric Qs = 40 kHz as usualcircles, 0.1 mm V = 160 mm/s offset to negate A_(n) = effects of ‘First5.125 J/mm² Pulse’ 50% Beam P = 82 W Scanned on Overlap Qs = 30 kHz samepowder v = 300 mm/s layer as A_(n) = previous 5.467 J/mm² profile scan.2 Circular profile. P = 82 W 100 μm −350 μm Powder laid 5 concentric Qs= 40 kHz as usual circles, 0.1 mm V = 160 mm/s offset to negate A_(n) =effects of ‘First 5.125 J/mm² Pulse’ 25% Beam P = 82 W Scanned onOverlap Qs = 30 kHz same powder v = 300 mm/s layer as A_(n) = previous3.644 J/mm² profile scan. 3 Circular profile. P = 82 W 100 μm −450 μmPowder laid 5 concentric Qs = 40 kHz as usual circles, 0.1 mm V = 160mm/s offset to negate A_(n) = effects of ‘First 5.125 J/mm² Pulse’ 0%Beam P = 82 W Scanned on Overlap Qs = 30 kHz same powder v = 300 mm/slayer as A_(n) = previous 2.733 J/mm² profile scan. 4 Waffle 0 and 90° P= 82 W  75 μm −525 μm Powder laid 700 μm Qs = 0 Hz (cw) as usuallinespacing v = 240 mm/s (−600% Beam A_(n) = overlap) 0.488 J/mm² 5Waffle 0 and 90° P = 82 W  75 μm −600 μm Powder laid 700 μm Qs = 0 Hz(cw) as usual linespacing v = 240 mm/s (−600% Beam A_(n) = overlap)0.488 J/mm² 6 Waffle 0 and 90° P = 82 W  75 μm −675 μm Powder laid 700μm Qs = 0 Hz (cw) as usual linespacing v = 240 mm/s (600% Beam A_(n) =overlap) 0.488 J/mm² 7 Waffle 45 and 135° P = 82 W  75 μm −750 μm Powderlaid 700 μm Qs = 0 Hz (cw) as usual linespacing v = 240 mm/s (−600% BeamA_(n) = overlap) 0.488 J/mm² 8 Waffle 45 and 135° P = 82 W  75 μm −825μm Powder laid 700 μm Qs = 0 Hz (cw) as usual linespacing v = 240 mm/s(−600% Beam A_(n) = overlap) 0.488 J/mm² 9 Waffle 45 and 135° P = 82 W 75 μm −900 μm Powder laid 700 μm Qs = 0 Hz (cw) as usual linespacing v= 240 mm/s (−600% Beam A_(n) = overlap) 0.488 J/mm²

The second and preferred approach uses a continuous scanning strategywhereby the pores are developed by the planar deposition of laser meltedpowder tracks superimposed over each other. This superimpositioncombined with the melt flow produces random and pseudorandom porousstructures. The properties of the final structure, randomness,interconnectivity, mechanical strength and thermal response arecontrolled by the process parameters employed. One set of scanningparameters used was: Scanning sequences of 0° 0°0°, 90° 90° 90°, 45° 45°45°, 135°, 135°, 135°, of layer thickness 0.1 mm were developed to forma waffle. Three layers of each were necessary to obtain sufficient webthickness in the “z” direction. The array of sequences was repeated manytimes to give a construct of the desired height. Laser power was 82watts, operating frequency between 0 (cw) and 40 KHz, scan speed ofbetween 160 and 240 mm/sec with a beam overlap of −700%. FIG. 31 showssuch a construct.

The use of an optical inspection method to determine this approximateporosity is appropriate given the sample size. This method, although notaccurate due to the filter selection process, can, if used carefully,provide an indication of porosity. An average porosity level of around25% was predicted. This porosity level falls within the range of thedesired porosity for bone in-growth structures.

In consideration of the potential application, it is important tominimize loose surface contamination and demonstrate the ability tofully clean the surface. Laser cleaning or acid etching technique may beeffective. Additionally, a rigorous cleaning protocol to remove allloose powder may entail blowing the porous structure with clean drycompressed gas, followed by a period of ultrasonic agitation in atreatment fluid. Once dried, a laser scan may be used to seal anyremaining loose particles.

On examination, all candidate materials and substrates were selectivelyfused to produce a complex interconnected pore structure. There weresmall differences in certain process parameters such as speed and beamoverlap percentage. From FIG. 12 it can also be seen how the Ti buildhas successfully fused with the Ti alloy substrate using a laser powerof 82 W cw, beam overlap of −40% and a laser scanning speed of 180mms⁻¹. With the ability to produce structures with a controlledporosity, this demonstrates how the Direct Laser Remelting process canbe used as a surface modification technology. Certain metal combinationsinteracted unfavourably and resulted in formation of intermetallics,which are inherently brittle structures. To overcome this problem it maybe necessary to use a bond coat with the substrate. It is then possibleto build directly on to the substrate with a porous build. A typicalexample of the use of a bond coat is provided by the combination oftitanium on to a cobalt chromium substrate. Tantalum also was aneffective bond coat in this example. Note that the bond coat may beapplied by laser technology, but other methods are also possible such asgas plasma deposition.

The non-contact surface profilimeotry (OSP) images shown in FIGS. 13A to13D show the surface profile. In addition, the Surface Data shown inFIGS. 14A and 14B and 15A and 15B show a coded profile of the plan viewsof the samples. FIG. 14A shows Ti on Ti (OSP Surface Data) where v=200mms-¹, FIG. 14B shows CoCr on Ti (OSP Surface Data) where v=200 mms-¹,and FIG. 15A shows Nb on Ti (OSP Surface Data) where v=200 mms-¹ andFIG. 15B shows Ta on Ti (OSP Surface Data) where v=200 mms-¹.

FIGS. 16A to 25 are scanning electron microscope (SEM) micrographs of aseries of single layer Ti on CoCr and Ti on Ti images that were producedprior to the multi-layer builds shown in FIGS. 8 and 9 respectively andas follows.

FIG. 16A shows Ti on CoCr (Single Layer; SEM Micrograph) v=160 mms-¹;

FIG. 16B shows Ti on CoCr (Single Layer; SEM Micrograph) v=160 mms-¹;

FIG. 17A shows Ti on CoCr (Single Layer; SEM Micrograph) v=170 mms-¹;

FIG. 17B shows Ti on CoCr (Single Layer; SEM Micrograph) v=180 mms-¹;

FIG. 18A shows Ti on CoCr (Single Layer; SEM Micrograph) v=190 mms-¹;

FIG. 18B shows Ti on CoCr (Single Layer; SEM Micrograph) v=200 mms-¹;

FIG. 19A shows Ti on CoCr (Single Layer; SEM Micrograph) v=210 mms-¹;

FIG. 19B shows Ti on CoCr (Single Layer; SEM Micrograph) v=220 mms-¹;

FIG. 20A shows Ti on CoCr (Single Layer; SEM Micrograph) v=230 mms-¹;

FIG. 20B shows Ti on CoCr (Single Layer; SEM Micrograph) v=240 mms-¹;

FIG. 21A shows Ti on Ti (Single Layer; SEM Micrograph) v=160 mms-¹;

FIG. 21B shows Ti on Ti (Single Layer; SEM Micrograph) v=170 mms-¹;

FIG. 22A shows Ti on Ti (Single Layer; SEM Micrograph) v=190 mms-¹;

FIG. 22B shows Ti on Ti (Single Layer; SEM Micrograph) v=200 mms-¹;

FIG. 23A shows Ti on Ti (Single Layer; SEM Micrograph) v=220 mms-¹;

FIG. 23B shows Ti on Ti (Single Layer; SEM Micrograph) v=230 mms-¹;

FIG. 24A shows Ti on Ti (Single Layer; SEM Micrograph) v=240 mms-¹;

FIG. 24B shows Ti on Ti (Single Layer; SEM Micrograph) v=240 mms-¹;

The method according to the present invention can produce surfacestructures on all powder/baseplate combinations with careful selectionof process parameters.

As described above, the process is carried out on flat baseplates thatprovide for easy powder delivery in successive layers of around 100 μmthickness. Control of powder layer thickness is very important ifconsistent surface properties are required. The application of thistechnology can also be applied to curved surfaces such as those found inmodern prosthetic devices; with refinements being made to the powderlayer technique.

The structures have all received ultrasonic and aqueous cleaning. Onclose examination, the resultant porous surfaces produced by the DirectLaser Remelting process exhibit small particulates that are scatteredthroughout the structure. It is unclear at this stage whether theseparticulates are bonded to the surface or loosely attached but there aremeans to remove the particulates if required.

The Direct Laser Remelting process has the ability to produce porousstructures that are suitable for bone in-growth applications. Thepowdered surfaces have undergone considerable thermal cyclingculminating in rapid cooling rates that have produced very finedendritic structures (e.g. FIGS. 13A to 13D).

The Direct Laser Remelting process can produce effective bone in-growthsurfaces and the manufacturing costs are reasonable.

In the preceding examples, the object has been to provide a porousstructure on a base but the present invention can also be used toprovide a non-porous structure on such a base to form athree-dimensional structure. The same techniques can be utilized for thematerials concerned but the laser processing parameters can beappropriately selected so that a substantially solid non-porousstructure is achieved.

Again, a technique can be used to deposit the powder onto a suitablecarrier, for example a mold, and to carry out the process without theuse of a base so that a three-dimensional structure is achieved whichcan be either porous, as described above, or non-porous if required.

Additionally, the porosity of successive layers of powder can be variedby either creating a specific type of unit cell or manipulating variousdimensions of a given unit cell.

There have been a number of studies to determine the optimum porestructure for maximization of bone in-growth on prostheses. The generalfindings suggest that optimum porosity is between approximately 20% and40%, and aim to mid value with a mean volume percent of voids of about70%. The preferred pore structure is interconnected, with a minimum poresize between about 80 μm and 100 μm and a maximum pore size between 80μm and 800 μm. The structured thickness for in-growth is 1.4-1.6 mm, butcan be larger or smaller depending on the application.

In the present invention porous structures are built in the form of aplurality of unit cells. Many designs of unit cells are possible to givethe shape, type, degree, and size of porosity required. Such unit celldesigns can be dodecahedral, octahedral, diamond, as well as many othervarious shapes. Additionally, besides regular geometric shapes asdiscussed above the unit cells of the present invention may beconfigured to have irregular shapes where various sides and dimensionshave little if any repeating sequences. The unit cells can be configuredto constructs that closely mimic the structure of trabecular bone forinstance. Unit cells can be space filling, all the space within athree-dimensional object is filled with cells, or interconnected wherethere may be some space left between cells but the cells are connectedtogether by their edges.

The cells can be distributed within the construct a number of ways.Firstly, they may be made into a block within a computer automateddesign system where the dimensions correspond to the extent of the solidgeometry. This block can then be intersected with the geometryrepresenting the component to produce a porous cellular representationof the geometry. Secondly, the cells may be deformed so as to drape overan object thus allowing the cells to follow the surface of the geometry.Thirdly, the cells can be populated through the geometry following thecontours of any selected surface.

The unit cell can be open or complete at the surface of the construct toproduce a desired effect. For instance, open cells with truncatedlattice struts produce a surface with a porosity and impart the surfacewith some degree of barb.

Modifying the lattice strut dimensions can control the mechanicalstrength of the unit cell. This modification can be in a number of keyareas. The lattice strut can be adjusted by careful selection of buildparameters or specifically by changing the design of the cross-sectionof each strut. The density of the lattice can similarly be adjusted bymodification of the density of the unit cells as can the extent andshape of porosity or a combination thereof. Clearly the overall designof the unit cell will also have a significant effect of the structuralperformance of the lattice. For instance, dodecahedral unit cells have adifferent mechanical performance when compared to a tetrahedral(diamond) structure.

As shown in FIGS. 32A and 32B, in a tetrahedron 8, each point 10, 12,14, and 16 is the same distance from the neighboring point. Thisstructure is analogous to the arrangements of the carbon atoms indiamond.

Each carbon atom in the diamond is surrounded by four nearest neighbors.They are connected together by bonds that separate them by a distance of1.5445 angstroms. The angles between these bonds are 109.5 degrees. As aresult, the central atom and its neighbors form a tetrahedron. Thisgeometry as in the case discussed herein may then be scaled toappropriate value for the pore construct required.

The two key parameters used to define the relations regarding height,surface area, space height, volume of tetrahedron, and the dihedralangle of a tetrahedron are the strand length of the tetrahedron and,i.e., the diameter or height and width, cross section area of the strandi.e., strut. These two parameters control the pore size and porosity ofthe structure. The parameter editor and relation editor within a typicalCAD system can be used to control these parameters. Hence, by changingthe parameters one can change the fundamental properties of the porousstructure. As shown in FIGS. 32A and 32B, the diamond structure may havea circular cross-section strands or square cross-section strands.Although only two strand cross-sections are illustrated, strands havingvarious cross-sections are possible. Further, this is true with most ofthe designs for the unit cell.

To create the mesh as shown in FIG. 32C, the unit cell can be instancedacross the 3-D space to produce the required lattice. FIG. 33illustrates a view of a diamond lattice structure with and without laserbeam compensation. Laser beam compensation essentially allows thediameter of the beam to be taken into account. Without it theconstructed geometry is one beam diameter too wide as the beam tracesout the contour of the particular section being grown. When laser beamcompensation is utilized, the contour is offset half a beam diameter allaround the constructed geometry which is represented in the CAD file.Although various parameters may be used, the parameters employed tocreate the lattices of FIG. 33 include a laser power of 90.5 watts withan exposure time of 1,000 μsec from a point distance of 90 μm. Table 1illustrates various other examples of parameters that may be used tocreate various unit cells.

TABLE 1 edge laser point length diameter power exposure distance Partbuild on SLM μm μm Watts μsec μm Diamond Structure 2000 200 90.5 1000 90Diamond Structure with 2000 200 90.5 1000 90 compensation DodecahedronStructure 1500 200 68.3 1000 90 Dodecahedron Structure 1500 200 68.31000 90 with compensation Modified Truncated 1500 200 90.5 1000 90Octahedron

As shown in FIGS. 34A and 34B, the porous structure can also be createdusing a unit cell in the shape of a dodecahedron. The regulardodecahedron is a platonic solid composed of 20 polyhedron vertices, 30polyhedron edges, and 12 pentagonal faces. This polyhedron is one of anorder of five regular polyhedra, that is, they each represent theregular division of 3-dimensional space, equilaterally andequiangularly. This basic unit cell for a decahedron mesh can be builtup in a CAD package using the following calculations and procedure. Thedodecahedron has twelve regular pentagonal faces, twenty vertices, andthirty edges. These faces meet at each vertex. The calculations for aside length of a dodecahedron are given by simple trigonometrycalculations and are known by those in the art.

In a method of use, a sweep feature is first used to model thedodecahedron structure by driving a profile along a trajectory curve.The trajectory curves are constructed from datum points corresponding tothe vertices of the dodecahedron connected by datum curves. The type ofprofile remains constant along the sweep producing the model shown inFIG. 34A. The size and shape of the profile can be designed to suit theparticular application and the required strut diameter. Once aparticular unit cell has been designed, the cell can be instanced toproduce a regular lattice as shown in FIG. 34B. As a dodecahedron is notspaced filling, meshes are produced by simple offsetting of the unitcell and allowing some of the struts to overlap. This method ofoverlapping may be used with the alternate shapes of the unit cell.

FIG. 35 shows a view of a dodecahedron (with and without laser beamcompensation, from left to right) structure using selective lasermelting process parameters. Once again, although the parameters may bevaried, the lattices of FIG. 35 were created using the followingparameters; a laser power of 90.5 watts, exposure of the powder for1,000 μsec and a point distance of 90 μm.

As shown in FIGS. 36A and 36B, the unit cell of the present inventionmay also be constructed in the shape of a truncated octahedron. Atruncated octahedron has eight regular hexagonal faces, six regularsquare faces, twenty-four vertices, and thirty-six edges. A square andtwo hexagons meet at each vertex. When the octahedron is truncated, itcreates a square face replacing the vertex, and changes the triangularface to a hexagonal face. This solid contains six square faces and eighthexagonal faces. The square faces replace the vertices and thus thisleads to the formation of the hexagonal faces. It should be noted herethat these truncations are not regular polyhedra, but rathersquare-based prisms. All edges of an Archimedean solid have the samelength, since the features are regular polygons and the edges of aregular polygon have the same length. The neighbors of a polygon musthave the same edge length, therefore also the neighbors and so on. Aswith previous unit cells, various dimensions such as the octahedronheight, octahedron volume, octahedron surface area, octahedron dihedralangle, and truncated octahedron volume, truncated octahedron height,truncated octahedron area, truncated octahedron volume, truncatedoctahedron dihedral angle can be determined by simple trigonometry andare known by those skilled in the art.

In a method of use, a CAD model of the truncated octahedron isconstructed using the sweep feature and calculations and dimensions areincorporated using basic trigonometry. Two tessellate the unit cell, theunit cell is first reoriented to enable easy tessellation and to reducethe number of horizontal struts in the model. Further, the model can bemodified to remove all of the horizontal struts as shown in FIG. 38A.The modified structure is reproduced in order to save file size in theStereolithography (“STL”) format of the program. Next, in order tocreate the unit cells, the method of using a laser melting process isperformed. In one preferred embodiment, the parameter chosen includes alaser power of 90.5 watts, an exposure of 1000 μsec with a pointdistance of 90 μm. FIG. 38B illustrates a lattice structure formed usinga plurality of individual truncated octahedron. As discussed earlier,the removal of various struts can create a barb effect on the exteriorsurface of the lattice structure.

As shown in FIGS. 39A-D, it is possible to reduce the size of the unitcell geometry. Also as shown, it is possible to manufacture open cellstructures with unit cell sizes below 1 millimeter. FIG. 39A illustratestruncated octahedron structures manufactured using the laser meltingprocess. All the structures were created using a laser power of 90.5 W,and a point distance of 90 μm; however, from left to right, the exposuretime was varied from 500 μsec and 100 μsec. FIG. 39B illustrates similarstructures and parameters as used with FIG. 39A, however, the unit cellused to create the lattice is diamond. FIGS. 39C and 39D illustrate aside view of the truncated octahedron structure of FIG. 39A and thediamond structure of FIG. 39B, respectively. Table 2 includes variousmanufacturing parameters used to construct various unit cell structure.

TABLE 2 Strand Length of Width of Laser Expo- Point Part build lengthstrand c/s strand c/s Power sure distance on SLM μm μm μm Watts μsec μmTruncated 3000 50 50 90.5 500 90 Octahedron Truncated 3000 50 50 90.5300 90 Octahedron Truncated 3000 50 50 90.5 100 90 Octahedron Truncated1000 50 50 90.5 500 90 Octahedron Truncated 1000 50 50 90.5 300 90Octahedron Truncated 1000 50 50 90.5 100 90 Octahedron Diamond  700 5050 90.5 500 90 Structure Diamond  700 50 50 90.5 300 90 StructureDiamond  700 50 50 90.5 100 90 Structure

Random representative geometries may be made from the current regularunit cells by applying a random X, Y, Z perturbation to the vertices ofthe unit cells. One such example can be seen in FIG. 40. In anotheraspect of the present invention, various freestanding constructs can begenerated. In a typical manufacturing procedure for the production of aconstruct, in this case a femoral hip component, the laser melting ofappropriate metallic powders is employed. Table 3 listed below, includesvarious examples of equipment and material used in the construct, aswell as typical software utilized.

TABLE 3 Equipment/Software Description Magics V8.05 (Materialise) CADsoftware package used for manipulating STL files and preparing buildsfor Rapid Manufacture (RM) Python Programming language MCP Realizer SLMmachine using 100 w fibre laser 316L gas atomized metal powder Metalpowder with an mean particle Osprey Metal Powders Ltd size ofapproximately 40 μm

In one example of this procedure an STL file of hip component 50 isloaded into an engineering design package such as Magics, as shown inFIG. 43A. The femoral attachment 51 may then be segmented from the body52 of the construct. The femoral attachment 51 may then be scaled downto 80% of its original size and reattached to the body 52 of the implant50 as shown in FIG. 44. This permits the implant to act as a structuralcore for the surface coating. The selection of the amount of scaling orindeed the design of the core allows for the production of the requiredstructural properties of the stem. Thus, the core may either be scaleddown even more or less to meet the required needs of the implant. ABoolean operation may next be performed in Magics to subtract thereduced femoral attachment from the original. This creates a “jacket” 56i.e., mold to be used as the interconnecting porous construct as shownin FIG. 45.

Jacket 56 is processed via a bespoke application that populates STLshapes with repeating open cellular lattice structures (OCLS). The OCLSused in this instance is a repeating unit cell of size 1.25 millimetersand strand diameter 200 μm. FIG. 46A illustrates a representation of asingle unit cell of the OCLS which will be used to populate jacket 56.The OCLS “jacket” 56 as shown in FIG. 46B will act as the porous surfacecoating of the femoral attachment 50. Once produced, the OCLS is slicedusing a bespoke program written in the Python programming language witha layer thickness of 50 μm. The main body of the construct is thenloaded into Fusco, a user interface for the MCP realizer. The file isthen prepared for manufacture by slicing the file with a 50 μm layerthickness and applying the hatching necessary for building solidconstructs. The component and OCLS femoral coating are then merged asshown in FIG. 47. The component may then be built on the SLM system asshown in FIG. 48A with typical process parameters being shown in table 4below.

TABLE 4 Slice height Power Exposure P_(dist) H_(dist) Feature (μm)(watts) (μs) (μm) (mm) Solid layer 100 90.5  800 80 0.125 Porous layer100 90.5 3500 N/a (spot) N/a

Although the present invention has been described with regard to thefemoral hip component as shown in FIG. 48A, the present invention mayalso be used to construct additional elements. For example, otherelements include an acetabular cup component illustrated in FIGS.49A-49C, augments from knee and hip surgery, FIGS. 50A and 50B, spinalcomponents FIGS. 51A-51C, maxillofacial reconstruction FIGS. 52A and52B, part of a special Nature, FIG. 53, and other additional irregularshapes such as that shown in FIG. 54. The list of illustrativecomponents above is only an example of various constructs which may becomposed using the method as disclosed herein and should be thought ofas being inclusive as opposed to exclusive.

In other aspect of the present invention an existing product may becoated with various metal layers and then scanned with a laser in orderto produce a finished product. In order to apply coating to existingproducts having either concave and/or convex profiles the presentinvention i.e., SLM requires the design of a special powder lay system.One such example was conducted and is shown in FIGS. 55A-59B.Specifically, a convex surface was created by using build apparatus 60as shown in FIGS. 55A-58. Build apparatus 60 includes a rotating piston62 and a cylinder onto which the convex surface 64 to be coated wasmounted. As the component rotates on the cylinder, it was made to dropin the Z-direction using platform 66 within the SLM machine. Powder 71was deposited onto the side of the component using a powder hopper 68and a wiper device 70 that runs up against the surface of the component.Once the correct amount of powder has been established a laser (notshown in the figures) in conjunction with a computer and variousprogramming packages, including those already discussed, were used toapply a laser beam to the powder in a predetermined manner. The powderwas deposited by hopper 68 and wiped to the correct height by wiperdevice 70. A full layer of metal powder was deposited by rotation of thecylinder through a full 360 degrees. However, the synthesis of the lasermelting process and the layer production process requires that only afraction of the circumference is layered and melted at any one time. Forexample, the method from production of a full layer would require thatthe service be built up from, possibly individual quarter revolutionsand melting steps as depicted in FIG. 59A. Preferably the laser meltingprocess is fast enough that the discreet stepping process tends to be acontinuous one with melting and rotation as well as layering occurringat the same time so as to increase throughput. FIGS. 55A-58 illustratethe sequence of operations with a final coated sample being shown inFIGS. 59A and 59B. In FIG. 59A, the lattice structure was built 3 mmthick and disposed against a 70 mm diameter steel hemisphere. In FIG.59B, the same hemisphere was used, but the lattice structure is 6 mmthick. FIGS. 60A-60B are CAD illustrations of the final assembly of aproduct component.

In an alternate embodiment of the present invention, the process can beparallelized by addition of many pistons and cylinder pairs around acentral laser beam. Optimal laser alignment to the surface can beachieved by a number of methods, including inclining the piston andcylinder pairs so the powder surface and the part surface are correctlyaligned normal to the laser beam. Typical operating parameters are shownin Table 5 below.

TABLE 5 Slice height Power Exposure P_(dist) H_(dist) (μm) (watts) (μs)(μm) (mm) 100 90.5 700 80 0.125

In another aspect of the present invention the laser produced porousstructure system may be used to manufacture a porous shell which thencan be inserted over a substrate and sintered in order to fixpermanently to the same. Some examples include the preparation of anacetabular cup component, a tibia knee insert component, and a femoralinsert as well as many additional products. In order to illustrate thisaspect of the present invention, reference will be made to the outerprofile of an acetabular component which serves as an inner profile of a“cap” to insure that an accurate fit is achieved when the cap is set onthe substrate (acetabular shell). The cup is built to a thickness of 1.5millimeters for example using a diamond configured construct to developthe interconnecting porosity. The metal powder used in one example isstainless steel. The processing parameters are shown in Table 6 listedbelow:

TABLE 6 Slice height Power Exposure P_(dist) H_(dist) (μm) (watts) (μs)(μm) (mm) 100 90.5 2000 N/a N/aHowever, the process parameters are dependent on the metal used and if adifferent metal, say for example, titanium was used, the parameterswould be different. FIGS. 61A-62B illustrate finished productsmanufactured by SLM.

In order to achieve a better and tighter fit of the cap over thecomponent, some adjustments to the geometry of the cap may beconsidered. For example, the inclusion of a rim 70 on the inner surfaceof the cap that interfaces with the groove 72 on the outer surface ofthe acetabular cup component 68 may be included. This mechanism acts asimple lock and gives both security and extra rigidity during thesintering process. Additional modifications may be utilized to improvecloseness of the fit and stability. For instance, the introduction of“snap-fits” which are apparent in everyday plastic components may beemployed to provide a more reliable attachment mechanism between the twoelements. Typical pads or center pads for both the femoral and tibialknee components can be produced by the SLM process and dropped orsnapped fit into place to the components and then sintered to attachfirmly to the underlying substrate. As previously stated, this techniquecan apply to other components where a porous outer surface is requiredto interface with either soft or hard tissue.

A further improvement in the mechanical and microstructural propertiesof the porous construct may be achieved by either conventional sinteringunder vacuum or inert atmosphere and/or hot isostatic pressing usingtemperature regimes known in the state of the art. As the constructspossess high density properties throughout their strands minimaldegradation in the structure of the construct is apparent.

In another aspect of the present invention, the appearance of the porousconstruct can be changed by the alteration of the processing conditionsor by the introduction of an acid etch process. For example, the laserpower or laser residence time may be reduced or a combination of bothwhich creates struts of the porous construct having a coating withlayers of unmelted metal particles firmly adhered to the strut surfaces.This has the effect of producing additional porous features that offer anew dimension to the overall porous structure of the construct. Suchfeatures are able to interact with cells in a different manner than themicrostructure imparted by the lattice construct and provide extrabenefits. A typical example of such construct with this satelliteappearance as depicted in FIG. 63 together with the processingparameters is employed. The structure illustrated in FIG. 63 was createdusing a laser power of 44.2 W and exposure time of 400 μsec. The metallayer thickness was 50 μm.

It is also possible to remove these satellites by an acid etchingprocess and a strong acid. The acid may consist of a mixture of 10milliliters of hydrogenfloride (HF), 5 milliliters of nitric acid (HNO₃)and 85 milliliters of H₂O. The HF and HNO₃ were respectively 48% and 69%concentrated. FIGS. 64 and 71 show the effects of such an acid's etchwith respect to time with the relevant conditions being noted. It can beseen clearly that the solids are moved to give a pure melted latticeconstruct. It is also clearly evident that the overall openness withinthe lattice is increased by the removal of the satellites. Additionally,prolonged exposure to the acid etch mix does result in some reduction instrut thickness which may also increase the lattice size further. Thisenables the production of struts having a reduced thickness to becreated by the STL method. Other acid types and combination may also beapplied to obtain similar results.

It will be appreciated that this method can, therefore, be used toproduce an article from the metals referred to which can be created to adesired shape and which may or may not require subsequent machining. Yetagain, such an article can be produced so that it has a graded porosityof, e.g., non-porous through various degrees of porosity to the outersurface layer. Such articles could be surgical prostheses, parts or anyother article to which this method of production would be advantageous.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method of producing a three-dimensionalporous structure comprising the steps of: depositing a first layer of ametal powder onto a substrate; scanning a beam at least once over thefirst layer of metal powder to melt the deposited first layer so as tocreate at least two solid portions separated from one another anddefining a pore having a required pore size within the porous structure;depositing successive layers of metal powder onto the first layer; andrepeating the scanning steps for each of the successive layers until adesired height of the porous structure relative to the substrate isreached, wherein the metal powder is selected from the group consistingof titanium, titanium alloys, stainless steel, cobalt chrome alloys,tantalum and niobium, wherein the repeating steps form a plurality ofpores having a pore size in a range from about 80 μm to 800 μm.
 2. Themethod of claim 1, wherein the repeating steps form a plurality ofpores, and wherein a minimum pore size of the pores is in a range fromabout 80 μm to 100 μm.
 3. The method of claim 1, wherein the repeatingsteps form a plurality of cells within the successive layers.
 4. Themethod of claim 3, wherein the cells are regular polygons.
 5. The methodof claim 3, wherein the cells are irregular polygons.
 6. The method ofclaim 3, wherein the repeating steps form struts defining the pluralityof cells.
 7. The method of claim 6, wherein the scanning steps includethe step of adjusting the beam to modify either one or both of across-sectional area and a length of the struts.
 8. The method of claim6, further comprising the step of applying a random perturbation in anydirection to vertices of the plurality of cells to randomize geometriesof the plurality of cells.
 9. The method of claim 1, wherein thesubstrate is a solid base or core.
 10. The method of claim 1, whereinthe porous structure is an orthopedic implant.
 11. The method of claim1, wherein the repeating steps include scanning the beam in angleddirections to other beam scans to create interconnecting pores.
 12. Themethod of claim 1, wherein the thickness of each of the first layer andthe successive layers is in a range from 5-2000 μm.
 13. A method ofproducing an orthopedic implant comprising: depositing a first layer ofa metal powder onto a substrate; scanning a beam at least once over thefirst layer of metal powder to melt the deposited first layer so as tocreate at least two solid portions separated from one another anddefining a pore having a required pore size within the orthopedicimplant; depositing successive layers of metal powder onto the firstlayer; and repeating the scanning steps for each of the successivelayers to form a plurality of polygonal cells within the orthopedicimplant the scanning steps being repeated until a desired height of theorthopedic implant relative to the substrate is reached.
 14. The methodof claim 13, wherein a minimum pore size of pores within the porousstructure is in a range from 80 μm to 100 μm.
 15. The method of claim13, wherein a maximum pore size is in a range from 80 μm to 800 μm. 16.The method of claim 13, wherein at least some of the plurality ofpolygonal cells define regular polygons.
 17. The method of claim 13,wherein at least some of the plurality of polygonal cells defineirregular polygons.
 18. The method of claim 17, wherein the polygonalcells defining irregular polygons are formed by applying a randomperturbation in any direction to vertices of corresponding ones of theplurality of polygonal cells.
 19. The method of claim 17, wherein atleast some of the polygonal cells are defined by at least one strut thathas an irregular cross-sectional shape.